Thermal cut-off devices are known which employ coil springs to achieve the necessary switching action in a thermal switching device when a thermally-fusible pellet melts. The use of separate springs and electrical contacts increases the component cost and the relative size and complexity of such a switching device. In the present invention, the required spring action and the necessary electrical contact between the leads are provided by a spiral spring which has an unexpanded inner diameter that is less than the outer diameter of a thermally-fusible pellet. The spring is expanded and fitted over the pellet and is held thereby so that a curved conducting projection at the end of the spiral spring is in contact with a mating curved conducting portion that is secured to the other lead. A thermally-sensitive switching device is thereby provided which has a reduced component court, is very small in size, is relatively inexpensive, and may carry a high current and may be assembled as either a normally open or a normally closed device.